Industrial emissions are a significant source of air pollution. In an attempt to limit the growth of such emissions, many industrialized countries have passed legislation. This legislation typically requires industries, whose emissions are potentially harmful to the environment, to take steps to monitor, control, and to treat the amount and types of emissions that are released into the environment. One such potentially harmful emission is ammonia. Thus, it is desirable to be able to measure the concentration of gaseous ammonia in a variety of environments. In particular, it is often desirable to continuously monitor gaseous ammonia in situ in environments such as flue gas streams, chemical plant feed streams and atmospheric backgrounds. In fact, it has been mandated to continuously monitor the ammonia concentration in flue gases resulting from deNOx processes that introduce ammonia to combustion products in order to convert oxides of nitrogen to N2 and H2O. In such processes, the level of ammonia that must be detected is as low as about 5 parts per million.
Monitoring and analyzing exhaust gases is complicated by the requirement that samples of the exhaust gas must often be taken from flue gas stacks before the exhaust gas is expelled into the atmosphere. Also, gas analysis is generally most conveniently conducted in an enclosed climate-controlled structure on the ground. The distance between sample taking and analysis is especially troublesome when flue gases must be monitored near the outlet of flue gas stacks that are hundreds of feet tall. The distance between gas sampling locations and gas analysis locations has resulted in a variety of conventional monitoring systems. In early monitoring systems, gas analysis equipment was housed at a convenient location on the ground and samples were periodically taken from a probe in the flue gas stack and physically carried to the analysis location. However, transporting samples is inconvenient and often dangerous. In addition, it is desirable in many processes to continuously monitor the components of a gas stream in real time. As mentioned, certain government regulations require continuous monitoring of exhaust gas streams.
In order to achieve continuous and convenient gas monitoring, stack sample probes have been connected to gas analysis equipment through long sample lines. In such systems, a pump near the gas analysis equipment creates suction in the long sample line that pulls gas into the sample probe and down the sample line to the pump whose outlet discharges sample gas into the gas analysis equipment. Continuous monitoring systems with such long sample transport lines are plagued by a number of gas monitoring inaccuracies. For example, when a heated gas sample taken from a flue gas stack is carried the length of a long sample transport line, the potential exists for the sample to cool and certain vapor phase constituents in the sample to condense in the sample transport line. This condensed liquid gathers on the walls of the transport line and collects at low points along the transport line. When a liquid condensate forms in the sample transport line, the condensed liquids tend to absorb gaseous contaminants in the line. Consequently, the absorbed gaseous contaminants will go undetected by the analysis equipment. In addition, the condensate may later emit the absorbed gases, or the condensate may react with a subsequent gas sample resulting in additional inaccuracies. Thus, once liquid forms in the sample transport line, accurate gas monitoring becomes difficult, if not impossible.
To overcome the problem of condensation formation in the sample gas transport line, some conventional systems insulate and heat the sample transport line to prevent condensation between the sampling location and the analysis location. However, gas transport line heaters are typically unreliable and have a tendency to malfunction. After such a malfunction is discovered, it is necessary to turn off the monitoring system and clean condensate out of the gas transport line. Such maintenance is both expensive and time consuming.
Another approach to overcoming the problems associated with long sample transport lines has been to move the gas analyzer to a location close to the gas sample probe. In such systems, the gas analyzer is sometimes mounted on the flue gas stack near the sample probe and the analysis results are transmitted to a convenient location where the results are displayed on a terminal and/or printed. Unfortunately, many gas analyzers are too large, or too sensitive, to be mounted on a flue gas stack and regular maintenance and calibration of gas analyzers is made inconvenient and costly by locating analyzers on the flue gas stack.
Another problem associated with long sample transport lines in conventional monitoring systems is that the gas samples are pulled from the sample probe to the analyzer under suction. If there are any leaks in the long sample transport line, the suction will pull ambient air into the sample creating inaccuracy and system contamination.
Therefore, there is need in the art for improved ammonia analyzers that are portable, more efficient and less expensive to operate.